Lateral transfer of mating system in Stemphylium

Area of Science:

• Mycology
• Evolutionary Biology
• Genetics

Background:

• The fungal genus Stemphylium comprises species that have transitioned from outcrossing to selfing reproductive strategies.
• Understanding the evolutionary mechanisms behind this transition, particularly the role of mating type (MAT) loci, is crucial.

Purpose of the Study:

• To investigate the origin and evolution of selfing in Stemphylium by analyzing their MAT loci.
• To compare MAT locus structures and phylogenies with organismal phylogenies to infer the history of reproductive modes.

Main Methods:

• Analysis of Stemphylium MAT loci (MAT1-1 and MAT1-2) and their structural variations.
• Phylogenetic analyses of MAT loci and multigene organismal data from 106 Stemphylium isolates.
• Comparison of MAT locus evolution with species phylogeny to identify origins of selfing.

Main Results:

• Some Stemphylium species possess fused MAT loci (MAT1-1 and MAT1-2), enabling selfing, similar to Cochliobolus.
• Phylogenetic analysis supports a monophyletic origin for these fused MAT regions.
• Organismal phylogeny reveals at least two independent origins of selfing, with identical fused MAT loci found in different clades, suggesting horizontal transfer.
• A third origin of selfing was identified in a group with only forward-oriented MAT1-1.

Conclusions:

• The fused MAT loci in Stemphylium likely originated once and were subsequently transferred horizontally among lineages.
• Multiple independent origins of selfing exist within the Stemphylium genus, involving both fused and non-fused MAT configurations.
• This study elucidates the complex evolutionary pathways leading to selfing in filamentous fungi.